Continuous heat treating of strapping and the like



Oct 4, 1966 o. c. TRAUTMAN 3,277,270

CONTINUOUS HEAT TREATING OF STRAPPING AND THE LIKE Filed April 9, 1965 2 Sheets-Sheet 1 INVENTOR. OSCAR C. TRAUTMAN ATTORNEYS Oct. 4, 1966 o. c. TRAUTMAN CONTINUOUS HEAT TREATING OF STRAPPING AND THE LIKE Filed April 9, 1965 2 Sheets-Sheet 2 I AH ho: Ik m PQaFZOO N A m N U VA WR ATTORNEYS United States Patent 3,277,270 CONTINUOUS HEAT TREATING OF STRAPPIN AND THE LIKE Oscar C. Trautman, 4040 Circlewood Drive, Cleveland, Ohio Filed Apr. 9, 1965, Ser. No. 446,968 7 Claims. (Cl. 219-155) This invention relates to continuous treating of steel strapping and the like by direct resistance heating.

A direct resistance heating operation for accomplishing desired heat treatment of strip, wire, rod and the like involves, basically, advancing longitudinally an indefinite length of such stock by power drive means and causing electric current to flow in a finite intermediate length of the material, whereby heat is produced in this length as a result of the ohmic resistance to such current flow. The stock may proceed in a single active length, for example, between a supply station and a take-up station, or in a number of parallel lengths or strands, and the electric current application is preferably realized by successively passing the material through spaced contact baths of molten metal or conductive salts serving as the electrical contact means. One of such baths can be utilized also for purposes of quenching, for example, immediately upon attainment of the maximum temperature of the heating of the material.

For safety and economy, it is desirable that shock hazard to workers be eliminated, together with any leakage to ground, and one arrangement serving these purposes utilizes a series of three spaced conductive baths, which arrangement permits both of the first and third baths of the series to be positively electrically grounded. However, in some installations a three-bath or three-span system on this order is not feasible, such as might be the case where available space is insuificient for this size of installation. There have, accordingly, been proposals for two-pan systems which do require insulation of the ungrounded bath and other safety features to eliminate the noted hazards, with these adding to the cost of the system as compared to one in which these elaborate precautions need not be taken.

It is a primary object of the present invention to provide method and apparatus for effectively neutralizing in a new and economical manner both end sections of a length of strapping and the likebeing treated by the described direct resistance technique.

Another object is to provide direct resistance heating method and apparatus for the treatment of steel strapping and the like in continuous operation by employment of two conductive baths, one being grounded, as contacts for electric current flow in the material and with blockage of any back current flow away from the ungrounded bath.

It is a further object of this invention to provide such a two-bath system in which the second bath is grounded and current flow from the energized first bath is eliminated from the incoming length of the material being treated.

It is also an object to provide such a two-bath system in which the noted current elimination at the entry side is automatically controlled and effective to cause a blocking counter electromotive force in the material proportional to and variable with any tendency of current to flow in the "ice various ways in which the principle of the invention may be employed.

In said annexed drawings:

FIG. 1 is a side elevational view of a two-bath direct resistance heat treating installation in accordance with the present invention; and

FIG. 2 is an electric wiring diagram illustrating the manner in which the aforesaid objectives are realized.

Referring now to the drawings in detail, the apparatus illustrated comprises an elevated contact bath 10 containing molten lead or another suitable conductive liquid and a longitudinally displaced second contact and quench bath 11 at a lower elevation.

The contact bath 10 has a fume collecting hood 12 in spaced relation thereabove which leads to a vent, and a comparable collector hood 13 is disposed over the quench bath 11. Each bath is of known construction and each is equipped with guide roll means, shown at 14 and 15 in association with the contact bath and at 16 and 17 within the quench bath. The latter is further equipped with a liquid circulating pump 18, with this also being a known feature.

Adjacent the entry end of the contact bath 10, there is an entrance drive roll assembly designated general-1y by the reference numeral 19, and the stock being treated is represented by a continuous line 20 which is advanced in the direction indicated by the arrowheads thereon, and could, for example, proceed from an appropriate festoon between the drive roll assembly and pay-01f reel structure, not shown. It is customary that several strands be advanced in parallel relation as earlier noted, and since the present improvements are particularly concerned with treating steel strapping, the line 20 will be considered for this purpose to represent a plurality of strips of such material moving from the entrance drive roll assembly 19 over an elevated idler 21 above the top of the contact bath, then downwardly at an angle into the bath 10 below the first roll means 14 at the entry end of this bath. The material, in this case the strapping, continues through the bath 10 and about the roll means 15 near the exit end of the same. From this last roll means, the strapping is brought up within a housing 22, over further roll means 23 therein, and then proceed-s downwardly at an angle through an elongated housing structure 24 to enter the quench bath 11 under the first roll means 16 in the latter. In such transfer of the stock from the contact to the quench bath, it is thus enclosed, and it is preferred that an inert gas atmosphere be provided in this enclosure. The strapping proceeds generally horizontally along the quench bath 11, in which the molten lead is circulated in operation, to the second roll means 17 near the distal end of this bath, and then upwardly through a vertical header 25 which is preferably filled with charcoal, or the equivalent, to wipe molten lead or the other conductive bath medium which might be employed from the strapping, with the thus removed liquid flowing back to the quench bath and stock carry loss of the liquid thereby being reduced. The strapping proceeds upwardly from the top of the header 25 over idler roll means 26, and then on to other fixtures not shown and not necessary for full understanding of this invention. By way of illustration, the strapping could, after leaving the installation described, proceed through a water quench, exit drive rolls, and finally to appropriate take-up reels.

The installation thus far described is known and, as also conventional, electric power from .a suitable source is applied to the contact and quench baths, with the latter being electrically grounded. Accordingly, electric current is caused to flow in the steel strapping or other material over that length extending from the surface of the con-tact bath to the surface of the quench bath, with this flow thus occurring essentially within the inert gas atmos- =2 phere provided and the material being quenched as it reaches the maximum temperature resulting from heating at the level of the electrical energy input and the ohmic resistance of .the strapping.

As will be appreciated, the application of voltage across the two baths, with the quench bath grounded, does entail in this system the possibility of current flow also in the incoming length of stock to the contact bath or reversely as compared to the direction of the advance, seeking a ground, and current flow in this entry section presents shock hazard. It is, therefore, normal in such a system to insulate and screen such incoming length and fixtures contacting the same. It has additionally been proposed to provide some supplemental protection designed to reduce the amount of back-flow of current by having an extremely long length of stock between the source of the material, such as the pay-off reels, and the contact bath to increase the impedance in such section, but this does not eliminate the hazard and still requires special insulating expedients to be employed. According to the present improvements, current flow in the strapping and the like in such incoming section is effectively blocked by the provision of an energized re-actance device designated generally by reference numeral 2 7 and shown in FIG. 1 as supported on a frame 28 arranged to surround the stock fed to the contact bath shortly before actual immersion therein.

The operation of the installation thus dis-closed is accomplished by the electric circuit of FIG. 2 in which line conductors 29 and 30 represent a conventional available source of electric energy. The application of the electric power to the conductive baths 10 and 11 in the manner set forth is shown as simply accomplished by lines 31 and '32, in which a suitable air circuit breaker 33 is incorporated, leading to the primary winding of a suitable step-down transformer 34. A conventional form of voltage regulator 35 is included in this primary supply circuit, and the primary winding may be provided, if desired, with a number of taps, an example of the primary voltage being approximately 460 volts. The secondary winding of this power transformer, which will provide a voltage on the order of from about 50 to 125 vol-ts, has its ends respectively connected to the contact bath 10 and the quench bath 11, as shown by the legends, with the latter electrically grounded.

The reactance device 27 which is provided to eliminate current flow in the incoming section of the strapping is here shown as in the form of a generally rectangular hollow magnetic core assembly 36, which can be formed of transformer iron laminations, with plural lengths of strapping 37 being treated shown as passing through this hollow core structure. It will be appreciated that current flow in these lengths of strapping from the energization of the contact bath 10 will produce electromagnetic flux in the thus surrounding core 36. At one side, the latter is provided with a winding 38 of multiple turns which is energized by connections respectively to a wiper contact 39 and one end of an associated variable resistan-ce device 40, the latter being connected at its ends to the lines 31 and 32 extending from the source to the power transformer 34 for the baths. This variable resistance device includes a reversible electric motor, not shown in elevation, but comprising the windings 4-1 and 42 operative, as will be explained, automatically to electrical series with the secondary of a reference transformer 47 having its primary similarly connected to the input lines 31 and 3 2, and the thus serially connected transformer windings are connected to opposite sides of a diode bridge rectifier 4 8. The remaining sides of this rectifier are connected in an output circuit including a choke coil 49, with a resistance 50 and capacitor 51 in parallel in a conventional filter arrangement as illustrated, and this circuit energizes a further feed-back potentiometer 52.

The movable arm of the potentiometer 52 is connected through a resistance 3 to the input circuit of an operational amplifier 54. A positive direct current voltage is provided at the terminal 56 to serve as a reference, with this voltage appearing across another poteniometer 56 the movable contact of which is likewise connected through a resistance 57 to' the input of the amplifier 54. This reference voltage input is also employed for bias of the amplifier 54 through a conventional circuit comprising resistance '58 and capacitor 5-9, and, at the output side of this amplifier, there is a further branch circuit including a potentiometer 60 and a series resistance 61. The movable contact arm of this last potentiometer 60 is connected through a resistance 62 similarly to the input to the operational amplifier, while the output across the circuit containing the potentiometer 60 and resistance 61, with the former providing control of the gain, is applied to a ratio detect-or shown as having amplifier sections 63 and 64, the outputs of which are applied to transformers 65 and 66. There is a third transformer 67 in series with the other two and connected as shown by the dashed line 68 to bridge the one motor 42, which has a series capacitance 69, and this motor winding is energized from a conventional alternating current supply represented by the terminal-s 70. The other winding 41 of the motor is connected, as shown, at one end to a center tap on the third transformer 68, and commonly at its other end to the transformers 65 and 66. V

In the operation of this system, the variable resistance 40 will ordinarily be set at a condition which should approximate that degree of energization of the winding 38 to produce a cancellation of the fiux expected to be generated in the core structure by current flow in the strapping 37. In the event that full cancellation is not satisfied or maintained, there will be a voltage induced in the sensing winding 43 and this voltage is applied to the input of the signal transformer 46. The thus produced voltage is in phase with the line reference voltage in the series reference transformer 47 and the sum of the two voltages is, of course, rectified in the bridge network 48, filtered, and applied to the feed-back potentiometer 52. The reference voltage derived from the potentiometer 56 is determined by adjustment thereof to equal the output appearing at the feed-back potentiometer 52 without any signal factor in the latter derived as set forth. When the feed-back voltage exceeds this reference voltage, the input to the operational amplifier 54 will assume a proportional negative value, and this voltage is amplified and presented to the ratio, detector 63, 64 as a positive error signal. By way of illustration, the p0sitive reference voltage can be within the range of from 0 to 45 volts and the feed-back voltage is in the range of from 0 to 45 volts, with an error signal within the range of from 0 to plus or minus 4.5 volts. This error signal will produce a current flow in the motor windings in such direction as to adjust the setting of the variable resistance 40 by drive of the wiper contact 39 in order to provide a higher voltage in the Winding 38 until the error signal is reduced to zero or complete cancellation of current flow in the strapping 37 has been realized.

In the event that the setting of the variable resistance 40 should be such that the winding 38 actually induces current flow in the strapping, then the signal transformer 46.will, through the sensing winding 43, receive a voltage out of phase with the reference line voltage from transformer 47, and this causes a voltage to be applied to the feed-back potentiometer 52 for addition to the reference voltage from potentiometer 56, with the input of a positive proportional voltage to the operational amplifier 54. In this circumstance, the amplifier output to the ratio detector 63, 64 will be in the form of a negative error signal, and a reverse current flow is caused in the motor winding such that its direction of rotation is relatively reversed and the resistance take off at the wiper 39 is changed to effect reduced energization of the core winding 38. Once again, this reverse operation will automatically proceed until the error signal is eliminated.

It is to be understood that as far as the heat treatment of the strapping and the like itself is concerned, only the simplest form of heat and quench procedure has been explained and is needed for appreciation of the nature of the present invention. There can be many known variations in this area, with the concern as above expressed to produce the current elimination in the incoming length or lengths of the material being treated. The energized reactance structure shown and described for this last purpose can comprise a single unit on such order or a plurality of comparable units serving simply to increase the efiects noted should this be desired or needed in a given installation. Moreover, although the sensing winding has been illustrated as disposed about a side of the hollow core structure, it can in fact be separate from the same and placed in other locations which might be more convenient and which would still permit this winding or coil to act as a detector in the manner and for the control described in detail.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

I therefore particularly point out and distinctly claim as my invention:

1. A method for the direct resistance heating of material such as steel strapping and the like, wherein the material is advanced longitudinally and heated during its continuous advancement comprising the steps of applying voltage to an instantaneous portion of the material through spaced first and second electric contacts engaging the material thereby creating current flow in the material and a heating thereof, electrically grounding the second contact to prevent current fiow in the material beyond said second contact and outside said portion of the material and inductively coupling a cancelling voltage into a section of the material beyond the first contact and outside said portion of the material to eliminate current flow in the material beyond this section.

2. The method set forth in claim 1 wherein the step of inductively coupling a cancelling voltage comprises the steps of detecting current flow in said section of the material, developing a signal proportional to the thus detected current flow and establishing a counter electromotive force acting inductively upon such section by such signal, with said force being effective to block the current flow in said section of the material.

3. The method set forth in claim 2 wherein the first and second electric contacts are conductive liquid baths and the second contact is also a quench bath and wherein the elimination of current flow in said section occurs prior to engagement of the material with the first bath.

4. The method set forth in claim 3 wherein the section of the material in advance of the first bath is passed through magnetic core structure in order that current flow in such section will produce flux in said structure, and said current flow is cancelled by establishing a proportional opposing flux in the core structure.

5. The method set forth in claim 4 wherein the phase and amplitude of current flow in said section in advance of the first bath is sensed and applied to control automatically the establishment of the opposing flux in the core structure.

6. Apparatus for the continuous heat treatment of material on the order of steel strapping and the like, comprising a pair of spaced electric contacts successively engaged by the material in longitudinal advance of the same, means for grounding one of said contacts, power means for applying a predetermined voltage across the pair of contacts to produce current How in the material, core structure associated with the length of material extending away from the ungrounded contact such that current flow in the material at this location produces flux in the core structure, winding means also associated with said core structure and effective when energized to produce flux in opposition to that established by such flow of current in the material, and control circuit means for regulating the energization of said winding means in order that the flux produced thereby is continuously eifective to cancel such current flow in said length of the material. 7. Apparatus as set forth in claim 6, including phase and amplitude sensing winding means for continuously surveying the current flow in said length of the material, means for establishing error signal voltage indicative of the lack of complete current cancellation, and means for applying said error signal to adjust the energization of the first named winding associated with the core structure to compensate such lack of cancellation.

References Cited by the Examiner ANTHONY BARTIS,

RICHARD M. WOOD, Examiner.

B. A. STEIN, Assistant Examiner.

Acting Primary Examiner. 

1. A METHOD FOR THE DIRECT RESISTANCE HEATING OF MATERIAL SUCH AS STEEL STRAPPING AND THE LIKE, WHEREIN THE MATERIAL IS ADVANCED LONGITUDIANLLY AND HEATED DURING ITS CONTINUOUS ADVANCEMENT COMPRISING THE STEPS OF APPLYING VOLTAGE TO AN INSTANTANEOUS PORTION OF THE MATERIAL THROUGH SPACED FIRST AND SECOND ELECTRIC CONTACTS ENGAGING THE MATERIAL THEREBY CREATING CURRENT FLOW IN THE MATERIAL AND A HEATING THEREOF, ELECTRICALLY GROUNDING THE SECOND CONTACT TO PREVENT CURRENT FLOW IN THE MATERIAL BEYOND SAID SECOND CONTACT AND OUTSIDE SAID PORTION OF THE MATERIAL AND INDUCTIVELY COUPLING A CANCELLING VOLTAGE INTO A SECTION OF THE MATERIAL BEYOND THE FIRST CONTACT AND OUTSIDE SAID PORTION OF THE MATERIAL TO ELIMINATE CURRENT FLOW IN THE MATERIAL BEYOND THIS SECTION. 